Incandescent lamp filament



y- 1934- w. BERGER 1,957,242

INCANDESCENT LAMP FILAMENT Original Filed Nov. 19, 1926 3 Sheets-Sheet l fig-. 1 .ELQA

Inventor:

y 1934- w. BERGER 1,957,242

y 1, 1934- w. BERGER 1,957,242

INCANDESGENT LAMP FILAMENT Original Filed Nov. 19. 1926 3 Sheets-Sheet A 3 fir/min Miller Eager Patented May 1, 1934 UNITED STATES PATENT OFFICE INCANDE SCENT LAlVIP FILALIENT Application November 19, 1926, Serial No. 149,515.

Renewed September 22, 1933.

October 22, 1925 2 Claims.

My invention relates to filaments for electric incandescent lamps.

One of the objects of my invention is to produce a filament from so-called long-crystal wire which will not distort or sag when burned in a lamp. My invention also contemplates certain novel forms of filaments particularly adaptable for projection lamps which require a concentrated filament structure.

Further features and advantages of my invention will appear from the following description of species thereof and from the drawings.

In the drawings, Fig. 1 is a side view of an electric incandescent lamp; Fig. 2 is a diagram matic view of an arrangement for bending a filament wire on a fiat mandrel, the latter being shown in an upright position in full lines and in a horizontal position in dotted lines, the inlet and outlet of the electric heating current being indicated by arrows; Figs. 3 and 4 are side views of filaments of special form and Fig. 5 is a front view thereof{ Figs. 6 and 7 are plan and front views respectively of a modified form of the filament shown in Figs. 3 to 5; Fig. 8 is a front view of a modification of Figs. 3 to 5 or 6 and '7 which is substantially circular in outline; Figs. 9 and 10 are side views of two further modifications of filaments having resilient lower portions allowing extension during glowing; Figs. 11 and 12 are diagrammatic side and front views respectively of another modification for cylindrically winding filaments, the cores between and around which said filament is wound being shown in dotted lines in Fig. 12 and in dot-dash lines in Fig. 11; Figs. 13 and 14 show a corresponding arrangement of a spherical filament; and Fig. 15 is a diagram of the mechanical tension of a wire wound according to the invention. I

According to my invention the bending radius of a so-called single-crystal or long-crystal filament wire is made so small that the sections of wire farthest from the neutral zone of bending are stressed far above the elastic limit of the wire, which is preferably tungsten, so that the wire takes a permanent set and does not return to its former position when the mandrel around which it is wound is removed, and also when the filament is heated to a white heat. Thus, when winding a filament of wire having a diameter of .0125 mm., a mandrel of circular section having a diameter of .05 mm. may be used. When using mandrels having sections other than circular the ratio of wire diameter and bending radius must be proportionately selected, that is, when using a wire having ,a diameter of .0125'mm. the bend-.

In Germany ing radius must be approximately .025 mm. in at least one point in each turn.

When a tungsten wire of .025 mm. diameter is coiled on a mandrel of .05 mm. diameter, the over-all length of the filament for 220 volts will be about 220 mm. Such a large filament results in a lowering of the efficiency in a gas-filled lamp due to the loss of light by convection and radiation. Therefore, according to my invention; in a lamp such as that of Fig. 1 comprising a bulb a, base b, filament c and lead wires d and f, the said filament 0 may be wound on a mandrel g (Fig. 2) of rectangular cross-section, said filament wire 0 being heated by passage of an electric current therethrough. In this way a coiled filament may be made for 220 volts and 200 watts capacity with an over-all length of not over 35 mm. Thus by using corresponding mandrels it is possible to make filaments for 220 volt gasfilled lamps with losses by convection and radiation approximately equal to those of 110 volt lamps so that both lamps will have approximately the same light intensity for the same voltage.

Furthermore, long crystal wires of diameters greater than those used to date may be advantageously used, e. g., wires having diameters of .4 to .9 mm. or more may be wound around mandrels of circular cross-section, the resulting filaments being free from distortion and sagging.

With such wires, the bending moment of which is very great, the bending radii may be somewhat greater in proportion to the diameters of the wires than stated above.

By bending long-crystal wire according to my invention around a radius of curvature sufiiciently small to cause the wire to be strained beyond the elastic limit and take a permanent set, filaments may be made for use, for example, on 110 volts with a capacity of 7000 watts.

Filaments operating at a high Wattage are preferably arranged in lamps'so that thelower part may settle when glowing without sagging or crowding together. Figs. 9 and 10 show two such constructions. .In Fig. 9 the coiled filament m is suspended on a lead 11 while the lower lead 0 is yieldingly arranged by being shaped in a U or a loop so that the filament m may settle when heated without causing adjacent turns to touch and be short-circuited.

The filament in Fig. 10 comprises two upright coils p, p suspended side by side on leads q and 1' respectively. The lower ends of the coils are connected to a cross wire s extending beyond each of said ends, the ends of said cross wire s engaging guides t, t". Collars or shoulders may be arranged at the ends of said cross wire s as shown in the drawings to prevent lateral movement thereof.

Lamps of very high intensity are required for use in beacons, aviation lighting, search lights, etc. For these purposes lamps may be provided with filaments according to the present invention so constructed that the turns of the filament are crowded closely together without appreciable overlapping of lighting areas in the direction of projection. This is done by staggering parts of the filament in the direction of projection.

Referring to Figs. 3 to- 5, the filament h is formed in sections each comprising a wavy line, the crests of the waves of one section being located opposite the troughs of the adjacent section. For a lamp of 6000 watts and 110 volts, a tungsten wire of .8 mm. diameter, and 1200 mm. long is required. By using a radius of 1.4 mm. for the waves and making each section 20 mm. long, the projecting surface may be reduced to about 20 mm. by 30 mm, thus producing a light source of 600 square millimeters. The ratio of the maximum to the spherical intensity of light being very high, the input may be fixed at about .2 watt per standard candle in the direction of highest intensity of light. The lamps will have about 30,000 candlepower with about 50 candlepower per square millimeter of lighting surface at right angles to the direction of projection.

The filament wire may be waved in the following manner:

A number of mandrels corresponding to the number of half waves desired (five in Figs. 3 and 4), and having a suitable diameter, say 2.8 mm. for a wire of .8 mm. diameter, are arranged in a straight row parallel to one another with a distance equal to the diameter of the wire between successive mandrels. The wire is wound half way around the top mandrel, then half way around the next mandrel in the opposite direction and so on to the bottom mandrel around which it is completely wound, thence half way around each of the successive mandrels upward and so on. The crests and troughs of adjacent waves are thus arranged opposite each other. The resulting filament provides a concentrated light source of high intensity. The half waves need not, of course, be semi-circular in shape.

In the form shown in Fig. 5, the waves are only seen when perceived from a direction oblique to the front of the filament, the sections appearing straight from the front. The intensity may be increased, therefore, by arranging the sections obliquely to the front, as shown in Figs. 6 and '7, preferably at an angle of approximately 45. The depth of the filament is decreased in this manner. Such filaments have given a light intensity of about twenty per cent greater than filaments constructed as in Fig. 1, and they may be operated on .2 watts per standard candle without shortening the useful life.

Instead of forming the filament in a square as shown in Fig. 5, it may be made more suitable for projection purposes by making it circular as shown in Fig. 8. The adjacent waved sections are made of varying lengths to produce the circular form. This may be done, for example, by increasing the length of successive sections from the outside toward the middle of half a wave.

Figs. 11 and 12 show diagrammatically how filaments are wound according to the invention into a cylindrical shape. Only a few cores or mandrels have been designated in order to show the shape clearly, whereas in reality more mandrels are used, being arranged closely together with a spacing only a little greater than the diameter of the filament wire so that the crests and troughs of the waves are arranged closely side by side. The mandrels u are arranged in a circle in a vertical plane (Fig. 12) and the filament wire 22 is wound around and between successive mandrels in a waved helical line.

The filament in Figs. 13 and 14 is of spherical shape. In the side view shown in Fig. 14 only the outer mandrels 101, 102, w:;, 7114 of a single spherical winding are shown. Fig. 13 is a plan View of the upper part of the filament on a larger scale than Fig. 14, the mandrels of the different windings being arranged vertically in concentric circles, each circle being for one winding of the filament so that the mandrels may be arranged side by side closely together with spacings between them of little greater distance than the diameter of the filament wire to be wound around and therebetween. The mandrels w are for the upper and lowermost windings of the spherical filament, the mandrels wz in a larger circle for the next windings toward the center and so on, the'mandrels 104 being for the largest circle at the middle.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. A filament for incandescent lamps of refractory metal wire comprising a plurality of parallel sections of wavy contour, the crests and troughs of adjacent sections being staggered with respect to one another.

2. A filament for incandescent lamps of refractory metal wire comprising a plurality of parallel sections of wavy contour, the planes defined by the major portion of each of said wavy parallel sections being inclined with respect to the main light projecting direction.

WALTER BERGER. 

